Welcome to the Hafezi Research Group

Recent advances in nanophotonic devices have enabled a variety of new technologies, including light-based classical information processing as a promising alternative to electronic signals in future circuits, non-classical light generation, and potential avenues for quantum information processing using light as a quantum bit. Our group aims to theoretically and experimentally investigate various quantum properties of light propagation and light-matter interaction for applications in classical and quantum information processing and sensing. Moreover, we explore associated fundamental phenomena, such as many-body physics, that could emerge in such physical systems.

Research Areas

Physicists classify and understand systems in terms of many properties; color, mass, length and microscopic symmetries are familiar examples. Another interesting feature is a system’s topology, or how its parts connect. As an example, a circular linked necklace can be deformed into an oval or a rectangle without changing the topology, since the links remain connected in the same way. But the necklace can only be made into the topologically distinct straight line if it is cut or its clasp is opened. In the 1980s physicists realized that some physical properties are entirely dictated by a system’s topology.

Our group investigates topological features in optical systems to explore new physics and develop optical devices with built-in protection. For more information, you can read the recent Quick Study in Physics Today.

When the interaction between particles in a physical system is weak, particles can be considered to act independently. In this situation, linear analysis such as band theory (coupled-mode theory) for electronic (photonic) systems is valid. However, when the interaction between particles is very strong, the quantum state of the system is no longer separable, and therefore, the system should be treated in its entirety. In our group, we explore quantum dynamics of strongly interacting photonic systems. In the context of quantum simulation, we investigate optical phenomena related to well-known effects in condensed matter physics such as quantum Hall physics and also lattice gauge theories. Moreover, we explore novel effects specific to optical systems, such as dissipative-driven phenomena.

More generally, we investigate how a many-body system can be theoretically characterized, e.g., entanglement spectrum, and efficiently prepared and probed in an experimental setting.

Controlling the interaction between quantum bits and electromagnetic fields is a fundamental challenge underlying quantum information science. Ideally, control allows storage, communication, and manipulation of the information at the level of single quanta. Unfortunately, no single degree of freedom satisfies all these criteria simultaneously. Instead, a hybrid approach may take advantage of each system’s most attractive properties. For example, optical photons provide a robust long-distance quantum bus, while microwave photons can be easily manipulated using superconducting qubits, and atoms can store quantum information for seconds or even minutes. In our group, we investigate various hybrid scenarios for applications in classical and quantum information processing and quantum simulation. Moreover, we exploit these hybrid approaches to probe and manipulate many-body quantum states, such as optical manipulation of electronic topological states.

Recently, we theoretically showed how to realize two-component fractional quantum Hall phases in monolayer graphene by optically driving the system. A laser is tuned into resonance between two Landau levels, giving rise to an effective tunneling between these two synthetic layers.

Topology plays a central role in the modern condensed matter, quantum information and high-energy physics. Certain Geometric manipulation of the manifold which supports a particular topological, known as the modular transformations, can be used as fault-tolerant logical operations in the context of both topological phases and topological quantum error correction codes. We realized that such transformations can be implemented in a single shot (i.e., with constant circuit depth), using local transversal SWAP operations between patches in a folded system with twist defects (wormholes in the synthetic dimension).

A promising near-term application of a quantum computer consisting of O(100) qubits is quantum simulation of fermionic systems, which exceeds the computational power of the world’s largest classical supercomputer due to the exponential growth of the Hilbert-space size. The target systems range f

Entanglement spectrum, the full spectrum of the reduced density matrix of a subsystem, plays a major role in characterising many-body quantum systems. In recent years, it has been widely studied in the fields of condensed matter physics, quantum information, high energy and black-hole physics.